Udam Jeong Si-han (1625∼1707) was a renowned scholar of the school of Toigye. Along with Galam Yi Hyeon-il, Jeong, who devoted his life to enhancing the legacy and ideas of Toigye Yi Hwang, was one of the two most representative leaders in spearheading the school of Toigye in the 17th century. His Sachilbyeonjeung in enormous volume was designed to explain the main purport of Toigye Confucianism and rebut external criticism. In a belief that an effort to promote Toigye Theory was equal to a commitment to defending it from criticism, he attempted to advocate Toigye Theory and give a correct guidance by criticizing Yulgok Theory. Sachilbyeonjeung is a counter-criticism against Yulgok's criticism against Toigye's Confucianism. Jeong was seemingly radical in his arguments, and there were some misunderstandings on Yulgok's thoughts. His assertions, however, were moderate compared with Yi Hyeon-il's criticism against Yulgok, consequently contributing to narrowing the gap between the school of Toigye and that of Yulgok. Such a paradoxical result is rarely found in the history of Confucianism in Joseon Dynasty. Taking a different perspective in evaluating Jeong Si-han, this study tries to close the gap between Jeong Si-han's thoughts and Yulgok's theory, which ultimately aims at amending the malady of partiality in Korean Confucianism.